DESCRIPTION: The primary goal of the proposed experiments on distortion-produc otoacoustic emissions (DPOAEs) is to investigate more completely particular issues that impact the field's fundamental understanding of several relatively recently developed measures of suppression and latency. An additional aim is t begin to identify the anatomical counterparts of the DPOAE-generation process. Specifically, one explicit goal is to determine if suppression-tuning curves provide a measure of cochlear trauma, or indication of the DPOAE generation site(s). Another specific aim is to determine the contribution that basal oute hair cells (OHCs) make to the observations in small laboratory animals and humans of suppression and enhancement of the DPOAE above the Q place. A furthe aim is to establish if systematically induced changes in DPOAE latency measure reflect alterations in cochlear filtering and/or build-up of the DPOAE-generation process. A final specific aim is to begin to determine if the status of the OFIC's stereocilia contribute to the viability of high-level DPOAE generator, and if the altered suppression tuning exhibited by some experimental animals following noise exposure is associated with more basally located regions of normal OHCs. The proposed studies will be performed in a parallel manner using both human and laboratory-rabbit subjects. The basic experimental plan is to make critical comparisons between DPOAEs generated in normal and pathological ears that have been temporarily or permanently altered by either exposure to excessive sounds or the administration of the ototoxic drug furosemide. The results of the planned experiments will contribute to out knowledge base concerning the basic processes underlying the production of DPOAEs, the identity of DPOAE measures that promise to be clinically useful, and the relevance of DPOAE generation in laboratory mammals to that in humans.